Baicalein has been used as a Chinese medicine, and is an abundant plant flavonoid present in fruits and vegetables. Here, we examined the effects of baicalein in adipogenesis and investigated its molecular mechanism in adipocytes. Baicalein lowered the intracellular lipid accumulation and decreased the transcription levels of the adipocyte-specific genes in mouse 3T3-L1 adipocytes. Glucose uptake mediated by glucose transporter 4 (GLUT4) was reduced, causing down-regulation of the intracellular lipid accumulation. These reductions were also observed even when baicalein was added in only early stage of adipogenesis (0&ndash;2 days) of 6-day-adipogenesis. Chromatin immunoprecipitation assay showed that baicalein decreased the binding level of C/EBP&alpha; protein to the promoter region of the GLUT4 gene. Phosphorylation of Akt at 1 h after the initiation of adipogenesis was inhibited by the treatment with baicalein. Inhibition during only the first 1.5 h after the initiation of adipogenesis by baicalein or an Akt inhibitor was enough to decrease the lipid contents in the cells undergoing adipocyte differentiation for 6 days. These results indicate that baicalein decreased the intracellular lipid accumulation by down-regulation of glucose uptake via repression of Akt-C/EBP&alpha;-GLUT4 signaling in the very early stage of adipogenesis of 3T3-L1 adipocytes.

pone.0163640.g001: Decrease in intracellular lipid accumulation in 3T3-L1 cells by baicalein.A, Structure of baicalein. B, Cell toxicity of baicalein toward 3T3-L1 cells. Cells were cultured for 6 days in DMEM containing various concentrations of baicalein (0–100 μM). Data are the means ± S.D. *p<0.05, as compared with the vehicle (0 μM). C, Oil Red O staining of baicalein-treated 3T3-L1 cells. Cells (undifferentiated cells: U) were differentiated into adipocytes (differentiated cells: D) for 6 days in DMEM without or with baicalein (0 or 50 μM). Intracellular lipid droplets were stained with Oil Red O. D, Baicalein-mediated suppression of the intracellular triglyceride level of 3T3-L1 cells. Cells (undifferentiated cells: U; white column) were differentiated into adipocytes (differentiated cells: D) for 6 days in DMEM without (gray column) or without baicalein (50 μM; black column). Data are presented as the means ± S.D. **p<0.01, as indicated by the brackets.

Mentions:
It has been reported that natural products lower adipogenesis [6]. Flavonoids are polyphenolic compounds that present in vegetables, fruits, and seeds [7]. They have protective effects against the various diseases [8]. Baicalein (4′,5,7-trihydroxyflavone; Fig 1A) is a plant flavonoid isolated from the roots of Scutellaria baicalensis [9]. It is present abundantly in most plants such as fruits and vegetables [10], and it has various biological and physiological activities such as anti-cancer, anti-inflammatory, and antioxidant ones [11, 12]. Although baicalein has a variety of biological activities, the functions of baicalein and its regulatory mechanism in adipose cells remain unclear.

pone.0163640.g001: Decrease in intracellular lipid accumulation in 3T3-L1 cells by baicalein.A, Structure of baicalein. B, Cell toxicity of baicalein toward 3T3-L1 cells. Cells were cultured for 6 days in DMEM containing various concentrations of baicalein (0–100 μM). Data are the means ± S.D. *p<0.05, as compared with the vehicle (0 μM). C, Oil Red O staining of baicalein-treated 3T3-L1 cells. Cells (undifferentiated cells: U) were differentiated into adipocytes (differentiated cells: D) for 6 days in DMEM without or with baicalein (0 or 50 μM). Intracellular lipid droplets were stained with Oil Red O. D, Baicalein-mediated suppression of the intracellular triglyceride level of 3T3-L1 cells. Cells (undifferentiated cells: U; white column) were differentiated into adipocytes (differentiated cells: D) for 6 days in DMEM without (gray column) or without baicalein (50 μM; black column). Data are presented as the means ± S.D. **p<0.01, as indicated by the brackets.

Mentions:
It has been reported that natural products lower adipogenesis [6]. Flavonoids are polyphenolic compounds that present in vegetables, fruits, and seeds [7]. They have protective effects against the various diseases [8]. Baicalein (4′,5,7-trihydroxyflavone; Fig 1A) is a plant flavonoid isolated from the roots of Scutellaria baicalensis [9]. It is present abundantly in most plants such as fruits and vegetables [10], and it has various biological and physiological activities such as anti-cancer, anti-inflammatory, and antioxidant ones [11, 12]. Although baicalein has a variety of biological activities, the functions of baicalein and its regulatory mechanism in adipose cells remain unclear.

Baicalein has been used as a Chinese medicine, and is an abundant plant flavonoid present in fruits and vegetables. Here, we examined the effects of baicalein in adipogenesis and investigated its molecular mechanism in adipocytes. Baicalein lowered the intracellular lipid accumulation and decreased the transcription levels of the adipocyte-specific genes in mouse 3T3-L1 adipocytes. Glucose uptake mediated by glucose transporter 4 (GLUT4) was reduced, causing down-regulation of the intracellular lipid accumulation. These reductions were also observed even when baicalein was added in only early stage of adipogenesis (0&ndash;2 days) of 6-day-adipogenesis. Chromatin immunoprecipitation assay showed that baicalein decreased the binding level of C/EBP&alpha; protein to the promoter region of the GLUT4 gene. Phosphorylation of Akt at 1 h after the initiation of adipogenesis was inhibited by the treatment with baicalein. Inhibition during only the first 1.5 h after the initiation of adipogenesis by baicalein or an Akt inhibitor was enough to decrease the lipid contents in the cells undergoing adipocyte differentiation for 6 days. These results indicate that baicalein decreased the intracellular lipid accumulation by down-regulation of glucose uptake via repression of Akt-C/EBP&alpha;-GLUT4 signaling in the very early stage of adipogenesis of 3T3-L1 adipocytes.